Interface Failure Mechanics of Elastically (Advanced Composite) Reinforced Steel Members

Tests on steel beams with adhesively bonded elastic reinforcing strips are used to deduce the mechanics of stress build up in the steel-to-strip interface up to failure. The solely elastic nature of the strips is a key concept in this study, as this elasticity leads to high interface stresses due either to nonlinear stiffness disparities between the steel and the reinforcing material when the steel yields, or to nonlinear geometric effects which are parasitic on this elasticity, including buckling of the strips and sharp section changes along the reinforced beam. Four features have been used in the tests to study these nonlinear effects, namely, multi-layer multi-length strips, imperfections in the adhesive, strips in both compression and tension, and tapering of the strip. The test results suggest that interface stresses may be sensitive to through-thickness variations of axial strain in the strips and to local variations of interface quality. Data from a nonlinear finite-element analysis, based on a novel two-layer interface element, are given for further insight into interface stress profiles. Conclusions are drawn on interface performance in the tests. Improved measurement strategies are suggested for shedding further light on the stress-transfer mechanics of this interface. The term connection is used synonymously with interface in this paper.